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/*
* Copyright 2017 Google
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#import <Foundation/Foundation.h>
NS_ASSUME_NONNULL_BEGIN
@protocol FSTRemoteDocumentCache;
@class FSTMaybeDocument;
@class FSTDocumentKey;
@class FSTWriteGroup;
/**
* An in-memory buffer of entries to be written to an FSTRemoteDocumentCache. It can be used to
* batch up a set of changes to be written to the cache, but additionally supports reading entries
* back with the `entryForKey:` method, falling back to the underlying FSTRemoteDocumentCache if
* no entry is buffered. In the absence of LevelDB transactions (that would allow reading back
* uncommitted writes), this greatly simplifies the implementation of complex operations that
* may want to freely read/write entries to the FSTRemoteDocumentCache while still ensuring that
* the final writing of the buffered entries is atomic.
*
* For doing blind writes that don't depend on the current state of the FSTRemoteDocumentCache
* or for plain reads, you can/should still just use the FSTRemoteDocumentCache directly.
*/
@interface FSTRemoteDocumentChangeBuffer : NSObject
+ (instancetype)changeBufferWithCache:(id<FSTRemoteDocumentCache>)cache;
- (instancetype)init __attribute__((unavailable("Use a static constructor instead")));
/** Buffers an `FSTRemoteDocumentCache addEntry:group:` call. */
- (void)addEntry:(FSTMaybeDocument *)maybeDocument;
// NOTE: removeEntryForKey: is not presently necessary and so is omitted.
/**
* Looks up an entry in the cache. The buffered changes will first be checked, and if no
* buffered change applies, this will forward to `FSTRemoteDocumentCache entryForKey:`.
*
* @param documentKey The key of the entry to look up.
* @return The cached FSTDocument or FSTDeletedDocument entry, or nil if we have nothing cached.
*/
- (nullable FSTMaybeDocument *)entryForKey:(FSTDocumentKey *)documentKey;
/**
* Applies buffered changes to the underlying FSTRemoteDocumentCache, using the provided
* FSTWriteGroup.
*/
- (void)applyToWriteGroup:(FSTWriteGroup *)group;
@end
NS_ASSUME_NONNULL_END
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